The present disclosure relates to semiconductor wafer probers, and more specifically, to adjusting an alignment between a probe card and a bridge beam of a wafer prober.
Testing semiconductor wafers includes electrically contacting a number of wafer contacts (e.g., 15,000) with microscopic contact pins. With a typical load of 10 grams (g) per pin, this sums up to transmitting a load of approximately 150 kilograms (kg) between the probe card comprising the contact pins and a rigid bridge beam mechanically coupled to and approximately aligned in parallel with the probe card.
In this common usage scenario, even small misalignments of (sub-) millimeter scale between probe card and bridge beam may cause inaccurate or defective electrical contacts. The external force causes the two members to move relative to each other, such that the gap separating them will get closed. When they come into physical contact with each other, they may move away from the prepared relative orientation and/or may become unable to assume a desired relative orientation for the case that the full load is applied. As a result, a chip which is actually free from defects may get classified as defective due to improper electrical contacting, or it may even get damaged in places where too large a pressure is applied during testing.
Adjusting the probe card and the bridge beam to a suitable, e.g. parallel, alignment is subject to dimensional tolerances. Especially the probe card may feature a local surface structure and/or a large scale misalignment, e.g. due to vertically arranged conducting strips, which prevents a precise relative parallel alignment with the bridge beam.